Among the desirable properties of a silver halide photographic element is high sharpness; that is, the element should enable faithful reproduction and display of both coarse and fine details of an original scene. Another desirable property of a photographic element is high overall sensitivity. This combination of properties has proven difficult to achieve in practice.
A general description of the difficulty in achieving high levels of sharpness may be found in T. H. James, ed., "The Theory of the Photographic Process," Macmillan, New York, 1977 and, in particular, at Chapter 20 of this text, pages 578-591, entitled "Optical Properties of the Photographic Emulsion" by J. Gasper and J. J. DePalma.
One method of improving sharpness, disclosed at U.S. Pat. Nos. 4,312,941 and at 4,391,884, involves the incorporation of a spatially fixed absorber dye in a film layer between the exposing light source and any layer comprising a conventional grain light sensitive silver halide emulsion sensitive to the region of the electromagnetic spectrum absorbed by the spatially fixed absorber dye. In these disclosures, the absorber dye is held spatially fixed either by means of a ballast group or by means of a mordanting material incorporated at a specified position in the film structure. Use of this spatial arrangement of absorber dye and emulsion reduces front-surface halation effects; that is, the spatially fixed dye absorbs light that has been reflected from an emulsion layer thus minimizing re-exposure at a position other than that intended. This positioning of spatially fixed dye has the difficulty that purposeful exposure is also attenuated and film sensitivity is degraded.
U.S. Pat. Nos. 4,746,600 and 4,855,220 disclose that larger degrees of sharpness can be attained by combining spatially fixed absorber dyes and Development Inhibitor Releasing Compounds (DIR Compounds) in a photographic silver halide recording material. The spatially fixed absorber dye is positioned between any emulsion layer sensitive to the region of the electromagnetic spectrum absorbed by the spatially fixed absorber dye containing layer and the exposing light source. This combination still suffers undesireably large degrees of film sensitivity loss.
U.S. patent application Ser. No. 869,987 filed Apr. 16, 1992 discloses that even larger improvements in sharpness can be attained by employing a spatially fixed absorber dye in a layer positioned between an exposure source and any layer comprising a sensitized high aspect ratio tabular shaped silver halide emulsion sensitized to the same region of the electromagnetic spectrum. Again, film sensitivity losses are encountered in this approach.
In a related area, U.S. Pat. Nos. 3,450,536; 3,663,228; 3,812,507; and 3,849,138 as well as British Patent GB 1,021,564 disclose the use of density layers placed between layers comprising emulsions sensitized to the same region of the electromagnetic spectrum for the purpose of increasing photographic latitude. The emulsions employed at the time of these publications were generally symmetrical and would today be described as having aspect ratios of about one. No mention is made in these publications of improved sharpness.
In yet another related area, U.S. Pat. No. 4,956,269 discloses that color reversal silver halide photographic elements incorporating tabular grain silver halide emulsions that have been developed using a reversal process can show improved sharpness under narrowly specified conditions. These conditions are met when the photographic color record incorporating the tabular grain silver halide emulsion also incorporates a quantity of absorber dye sufficient to reduce the sensitivity of that color record by at least 20%, when the total imaging layer thickness is less than 16 microns and when the swell ratio of the film is greater than 1.25. The materials described in this disclosure incorporate intermediate aspect ratio ( AR&lt;9.0) tabular grain silver halide emulsions. These conditions and constraints are non-predictive of the performance of color negative silver halide photographic materials. The absorber dyes described in this disclosure are solubilized dyes that distribute indiscriminantly throughout a film element. Large film sensitivity losses are again encountered in this approach.
U.S. patent application Ser. No. 869,675 filed Apr. 16, 1992 discloses that even larger degrees of sharpness improvement are attained when high aspect ratio tabular shaped silver halide grains are employed in combination with absorber dyes in a common layer, and that especially high degrees of sharpness enhancement are obtained when a color negative development process is employed in this case. The absorber dyes described in this disclosure are distributed indiscriminantly throughout a film element. Large film sensitivity losses remain inherent in this approach.